The invention relates to a device for reducing engine torque during shifting between gears in a gear transmission driven by the engine. Especially preferred embodiments of the invention include devices of this kind which are responsive only to engine speed and engine load conditions.
In such devices, the control expenditures are minimized because a switching signal from the gear is dispensed with and a shift operation is detected solely from the speed behavior, i.e. from the drop in speed of the internal combustion engine occurring when there is an up-shift. Also because the reduction in engine torque is limited to the full load range, at the high speeds of which the negative change in speed over time, which does not occur until during the up-shift, is relatively high and consequently is easier to measure. In a known device described in German Published Unexamined Application (DOS) No. 3,018,033 and corresponding to U.S. Pat. No. 4,370,904 overshoots which are produced from positive changes in speed over time and which may result in unintentional reduction in engine torque are not considered.
In a known device of another type described in German Patent Specification No. 2,842,389, the controlled variable causing the final control element to reduce the engine torque with a fixed delay occurs at the output of a timing element, the operating time of which is dependent on the engine load and, in addition, is zero if the engine speed is less than a limit value of, for example, 3000 rpm. When the limit value is exceeded, the operating time increases linearly with the speed. The set input of the timing element is connected to the output of an AND element, with which a signal occurs at one of its two inputs if a comparator circuit has detected that the engine speed is decreasing. At the other input, a signal occurs if the operating time has elapsed of a second timing element which is activated via its set input when an upshift occurs. Both timing elements are directly reset if a shift detection stage has recognized that a downshift is concerned. With this device, it is intended to achieve a reduction in jerky changes in speed, and thus the jerk in shifting, when a shift command occurs, whereby a minimum possible wear of the friction elements of the automatic change-speed gear is the aim.
Apart from the fact that a reduction in wear cannot be achieved to the desired extent in this known device because the reduction in engine torque cannot commence until after elapse of the operating time of the second timing element activated by the up-shift signal, the control effort or expenditure is high because, not only the control means dependent on the operating parameters of the internal combustion engine are necessary, but also control means for the processing and detection of gear shift signals are necessary.
An object on which the invention is based is the designing of a device of the generic above-described type with minimum possible effort and expenditure, such that the heat generation in the friction elements is decreased by a reduction in engine torque which is not to be perceived by the driver--in other words to be carried out within the operating time. However, it is to be avoided thereby that an unintended reduction in engine speed is triggered by overshoots, for example after sudden full acceleration out of the partial load range.
This object is achieved according to the invention by the provision of blocking circuit devices for blocking the engine torque reduction in response to detected positive rates of change over time of engine speed above predetermined values.
In the devices constructed according to preferred embodiments of the invention, overshoots with negative changes in speed over time, which may assume values which correspond to the values of a negative change in speed over time which also occur with up-shifts, are eliminated in their influence on the speed-dependent control means by monitoring of the positive changes in speed over time and blocking of the final control element for influencing the engine torque when critical acceleration values occur.
The blocked state with regard to the possibility of reducing the engine torque, triggered by such overshoots with initially positive change in speed over time in the devices constructed according to the invention are limited in time in accordance with certain preferred embodiments. However, the blocked state should last at least approximately for half a period of oscillation of the drive train natural frequency according to especially preferred embodiments of the invention.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.